Page 63 - North American Clean Energy March/April 2020 Issue
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        or corrosion damage to the raceways). Unfortunately, the techniques available
at the time proved insufficient to achieve such a durable coating at economical cost. It would be several more years before a special plasma coating process, known as physical vapor deposition (PVD), would make such bearings commercially viable.
PVD is a vacuum deposition method used to produce microthin films on objects such as machine parts. PVD employs physical processes including heating, sputtering, or transfer by laser or electron beam to produce a vapor of material. This vapor is then deposited on the object that requires coating.
By 2010, the first wind bearings leveraging PVD coatings began to populate the market. These bearings made use of a plasma-based PVD sputtering method, whereby atoms are ejected
by high-energy particles from a source material (the target), and transferred to a substrate (the bearing rollers).
How PVD Works
First, rollers are placed in a vacuum chamber and subjected to minute quantities of a special mixture of reactive gases, including Argon (Ar) and Acetylene (C2H2). In the presence of strong electric and magnetic fields, these gases react with the metallic target (commonly Tungsten carbide [WC]). The atoms from the
target are then dislodged by high-energy collisions; plasma ions bombard the source material, causing portions of it to ionize and condense on the surface of the object.
PVD is so precise, it essentially allows coatings to be deposited atom by atom. This microstructure control makes it possible to engineer coatings that possess the exact performance characteristics desired in an application. Compared to conventional bath or spray coatings, PVD coatings are more uniform and much more durable; in oil-out conditions, bearings with PVD coatings have been observed to last approximately 10 times longer than bearings with uncoated rollers.
When applied to bearing rollers, the PVD-coated surface acts as dissimilar material to the steel races, which minimizes friction. The coating is hard like a drill bit, yet slippery like a nonstick frying pan. This significantly reduces the likelihood of component scuffing, smearing, and wear as bearings rotate under extreme loads.
Years of Trouble-Free Service
PVD coatings are already proving effective in the field. Recently, in New Mexico, a 1.5 MW wind turbine using a mainshaft bearing with coated rollers was removed from service after seven years for re-powering. Bearing analysis showed little to no sign of adhesive wear on the raceways. In fact, the bearing was observed to be in “very good” condition for this stage of operation, despite the fact the bearing had not been relubricated in two years (in anticipation of the overhaul event). Furthermore, no evidence of progressive damage stages was found.
It was concluded, with a high degree of confidence, that the bearing would continue to operate into the 15- to 20-year time frame without issue. This was welcome news to the wind turbine owner because he was able to avoid the cost of a new mainshaft bearing entirely. Eliminating even one bearing replacement over the life of a turbine can save energy producers $100,000 or more, factoring in materials, labor, and logistics costs.
Innovation is Everywhere
Once restricted to a handful of laboratories, PVD methods have become widely available. Ongoing development has allowed the production of even more new coating types that can benefit machine components like wind bearings. In fact, wind turbine owners and builders have a growing inventory of coating options to consider when it comes to bearings, including coatings that offer tougher protection against corrosion, micropitting, and cracking.
Start a conversation with a trusted expert to learn more about engineered coatings—bearings that go the distance can have a big impact on productivity and profitability, from the smallest installations to the largest wind farms.
Vikram Bedekar is Materials Specialist, and Doug Lucas is Advanced Engineering Technologist for The Timken Company. Timken features a growing portfolio of engineered bearings and power transmission product brands.
The Timken Company ///
Strong and versatile crane
Manitowoc has launched the Potain MCT 325 to expand its MCT range of topless cranes.
The MCT 325 is designed to deliver easy transport and assembly, plus high efficiency and reliability on construction projects. Available in two versions, the MCT 325 offers jib length configurations from 40m up to 75m, in increments of 5m. The new model stays
true to the design characteristics of Potain topless cranes, with easy transport and erection combined with on-site performance. On a well- prepared site, the MCT 325 can be setup within 1.5 days, with the complete jib and counter-jib erected in four lifts. The MCT 325 is designed
to work with the 2m x 2m L68 and L69 mast systems and can be utilized with fixing angles in a regular high-rise construction; in an internal climbing configuration; or mounted on a chassis, giving users maximum versatility. There is also
a new square design of the crane’s counterjib.
To ensure easier assembly on site, the complete jib and counter-jib can be erected in two lifts each, meaning a greater choice of assist cranes can be used for the task. There are dedicated sling points on the counter jib and transport brackets on the jib to facilitate easier loading into the crane’s compact transport configuration. Customers have a variety of options for the hoisting, slewing, and trolley mechanisms. There are a variety of hoist options, all with frequency- controlled technology and the winches are available with a safety brake option.
The Manitowoc Company
       Figure 1. Bearings having rolling elements with engineered surfaces are often called wear-resistant bearings.
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